1. Field of the Invention
The invention relates to glassmaking furnaces, in particular the furnaces used in the manufacture of flat glass of the "float" type, and it relates more specifically to a method and a device intended to reduce the emission of NO.sub.x in the gaseous effluents discharged from the furnace.
2. Discussion of the Background
It is a concern of glassmaking furnace manufacturers to limit as much as possible the emissions of NO.sub.x in the combustion smoke, especially because of the fact that the standards are becoming increasingly demanding in this regard. These emissions should therefore be limited to 500 mg/M.sup.3 of NO.sub.x, a limit which the known methods do not allow to be obtained, or do allow, but to the detriment of their profitability.
The factors which influence the formation of NO.sub.x gases are known. These are essentially the temperature, since their emission increases exponentially above 1300.degree. C., or the excess air, since the NO.sub.x gases depend on the square root of the oxygen concentration, or else the N.sub.2 concentration.
A known method consists in causing a reducing agent to act on the gases emitted so that the NO.sub.x gases are converted into nitrogen. This agent may be ammonia, but the drawbacks of storing and handling such a substance are known. It is also possible to use a natural gas as reducing agent, but to the detriment of the consumption of the furnace.
It therefore turns out to be preferable to avoid these methods, and it has already been considered to adopt so-called primary measures, for example by preventing the formation of NO.sub.x within the flame itself, by reducing the excess combustion air. To do this, it was sought to limit the hot air which passes into the regenerator and to eliminate or decrease the inducted-cold-air intakes around the injectors in the unsealed furnace. It is thus possible to decrease the sprayed primary air by increasing the fuel-spraying pressure. For this purpose, it is necessary to provide a continuous control of the excess oxygen in the regenerator chambers and to use suitable fuel injectors. However, the results obtained remain insufficient and do not enable the percentage indicated above to be readily achieved.
Another primary measure consists in acting on the temperature. Thus, attempts may be made to modify the distribution of the fuel in order to reduce the maximum thermal level of the furnace, or to install suitable injectors in order to decrease the momentum of the fuel right to the limit of the appearance of unburnt gases in the discharge flue. It is also possible to use a spraying agent other than air, for example steam, when this is available.